Liquid-phase fluorinations involves the use of a mixture of corrosive reaction materials. The corrosion is acute, especially where Lewis-acid catalysts, such as antimony halide catalysts, are used under high reaction pressures and at elevated temperatures. Under these conditions, strong acids form which tend to corrode reactor vessels, even those comprised of corrosion-resistant materials such as Inconel 600, NAR25-50MII, Hastelloy C, Hastelloy G-30, duplex stainless steel, and Hastelloy C-22. Reactor corrosion compromises the structural integrity of the reactor and reduces its useful life.
Liquid-phase fluorinations also requires the constant input of heat. Traditionally, the amount of heat transferred to the reactor should be sufficient not only to drive the fluorinations reaction, but also to provide the heat necessary for distillation of the vapor product stream produced by the reaction. The heat for distillation and other post-reaction processing is transferred through the reactor vessel because the vaporized product stream generally is considered too corrosive for reboilers and other post-reaction heating apparatus. Conventional techniques for inputting heat to the reactor vessel include, for example, employing heating jackets and/or internal coils, and preheating and vaporizing the reaction materials.
For highly corrosive reactions, such as the synthesis of 1,1,1,3,3, pentafluoropropane (HFC-245 fa), traditional heat input techniques tend to be inadequate. Often, in such applications, the reactor vessel is lined with a corrosion-resistant fluoropolymer which unfortunately is a thermal insulator that impedes the transfer of heat into the reactor.
Aside from the problems of heat input into the reactor, it is frequently preferable to minimize heat flux or skin temperature in a reactor vessel containing corrosive reactants. The input of heat to a reactor vessel in excess of that needed for the reaction tends to vaporize catalyst and increase the corrosive nature of the product stream. Moreover, the additional heat leads to an increase in the thermal breakdown of reactants and/or products and in the formation of by-products.
Therefore, there is a need for a liquid-phase fluorinations system and method which minimizes corrosion while allowing for the controlled input of heat. The present invention fulfills this need among others.